JPH0493875A - Fixing roller and fixing device - Google Patents

Abstract

PURPOSE:To prevent offset from occurring and to obtain a device having excellent durability for a long time by specifying the volume specific resistance value of an elastic layer and the surface resistance value of a resin layer. CONSTITUTION:The surface resin layer 12 is provided on the elastic layer 11. The volume specific resistance value of the elastic layer 11 is set at <=10<7>OMEGAcm and the surface resistance value of the resin layer 12 is set at >=10<10>OMEGA and the thickness of the layer 12 is set at <=100mum. Then, offset performance is evaluated based on whether an image is transferred from a heating roller 1 to the half of the trailing edge side of a transfer material 211 as an offset image again by printing the horizontal line of two dots by spacing as much as five dots on the half of the leading edge side of the transfer material 211 in a feeding direction, so that the offset and a phenomenon such as the winding of the transfer material 211 are prevented from occurring and durable performance is made excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a fixing roller and a fixing device used in image forming apparatuses such as electrophotographic copying machines and printers.

[Prior art] Conventionally, a fixing roller used in a fixing device uses silicone rubber as an elastic layer, and on top of that is PTFE (tetrafluoroethylene resin) and PFA (tetrafluoroethylene/perfluoroalkoxyethylene copolymer). , rollers coated with a fluororesin such as FEP (tetrafluoroethylene/hexafluoropropylene copolymer) are known.

For example, Japanese Patent Publication No. 47-20747, Japanese Patent Application Publication No. 52-
No. 60145, Japanese Patent Application Laid-Open No. 52-96546, etc. disclose heating or pressure rollers for fixing which have a heat-resistant rubber layer covered with a fluororesin tube. Furthermore, in JP-A-57-89785, JP-A-58-27175, JP-A-61-170770, etc., a fluororesin layer is formed by coating a fluororesin on a heat-resistant rubber layer and then baking it. A heating or pressure roller for fusing is disclosed. Both of these improve the mold release property in order to compensate for the deterioration of the mold release property on the surface of the rubber layer due to long-term use.
The present invention aims to provide a heating or pressure roller for fixing with excellent durability by providing a fluororesin layer with excellent durability on the surface layer and making use of the elasticity of the rubber layer. In addition, in the above conventional example, since the resistance of the fluororesin layer and the rubber layer is high, the fixing roller becomes high potential due to frictional charging between the recording material and the fixing roller, and when the transfer material wraps around, the toner on the transfer material is electrostatically charged. There were problems such as offset occurring due to repulsion. The above phenomenon was particularly noticeable when this type of roller was used as the pressure roller.

As a technology to prevent such charging of the fixing roller,
For example, Japanese Patent Laid-Open No. 58-83878 discloses an elastic roller in which a mixture of fluororubber and fluororesin mixed with a conductive substance is coated on a rubber layer. The technique disclosed in this publication prevents the fixing roller from being charged by imparting conductivity to the surface release layer. Similarly, JP-A-64
Japanese Patent No. 24284 discloses a pressure roller in which a conductive PFA layer is provided as a surface release layer on an elastic layer.

[Problems to be Solved by the Invention] However, when the resistance of the conventional surface release layer was lowered, the following problems occurred.

In order to form a conductive fluororesin layer, it is necessary to mix a filler such as carbon black into the fluororesin layer, which reduces the mold releasability of the fluororesin layer. For this reason, the pressure roller is likely to become dirty due to long-term durability.

In addition, it is necessary to release the charge on the surface layer, and a static eliminating brush or the like must be provided.

Furthermore, in the case of an image forming apparatus having an image carrier and a transfer charger, if a high-resistance transfer material such as an OHP film is used, and if the surface fluororesin layer is made conductive, the pressure roller will not be charged. Although this can be prevented, the charge on the back side of the transfer material leaks from the front layer, weakening the ability of the transfer material to retain toner, resulting in offset.

[Means for Solving the Problems] The present invention, which solves the above problems, provides a fixing roller having a surface resin layer on an elastic layer, in which the volume resistivity of the elastic layer is 107 ΩCm or less, and the resin layer has a A fixing device characterized by having a surface resistance value of 1010 Ω or more and a thickness of 100 μm or less, and comprising a heating body and a pressure roller forming a nip with the heating body and having a surface resin layer on an elastic layer. The elastic layer has a volume resistivity of 10 7 Ωcm or less, and the resin layer has a surface resistance of 10 10 Ω or more and a thickness of 1100 LL or less.

[Embodiments of the invention] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a sectional view of the main parts of an image forming apparatus using a fixing device according to an embodiment of the present invention.

8 is a photosensitive drum on which an unfixed toner image is formed, and 9 is a transfer charger that transfers the toner image on the photosensitive drum 8 to a transfer material.

The heating roller has 1 core metal made of aluminum, SUS, iron, etc. 11
PTFE (tetrafluoroethylene) PFA (tetrafluoroethylene/perfluoroalkoxyethylene copolymer) on top
A resin layer 12 with good heat resistance and mold releasability such as PFA, FEP (tetrafluoroethylene - A coated tube 23 made of propylene hexafluoride copolymer is used. A temperature detector 3 such as a thermistor for detecting the surface temperature of the heating roller 1 is disposed around the heating roller 1, and a heater 4 for heating the heating roller 1 is provided at the center of the fixing roller 1. is installed. The surface temperature of the heating roller 1 is controlled to a predetermined value by blinking the heater 4 by a control section (not shown) based on a signal from the temperature detector 3.

An entrance guide 5 for guiding the transfer material to a nip portion between the heating roller 1 and the pressure roller 2 is provided at a transfer material entrance portion before the heating roller 1 and the pressure roller 2 . Furthermore, a separation claw 6 is provided on the surface of the heating roller 1 to separate the transfer material.

In such a fixing device, both the heating roller 1 and the pressure roller 2 have conductive metal cores that are grounded.

Next, the pressure roller 2 of this embodiment will be explained in more detail with reference to FIG. 1.

As mentioned above, the pressure roller 2 is coated with carbon black on a core metal 21 made of stainless steel, iron, or the like.

A silicone rubber layer 22 filled with metal, metal oxide, etc. and imparted with conductivity is provided, and a tube made of PFA or FEP is provided thereon as a resin layer 23. The conductive silicone rubber layer 22 preferably has a thickness of 2 to 10 mm and a hardness of 10 to 40 degrees (JIS A), and if the thickness is 2 mm or less or the hardness is 40 degrees or more (JIS A), it can be used as an elastic layer. The function of the resin layer 23 on the surface layer is not sufficient, and problems such as wrinkles are likely to occur in the paper passing performance of the transfer material. Wrinkles are more likely to appear on the skin. Further, the resistance value of the silicone rubber layer 22 is preferably 10 7 Ωcm or less in terms of volume resistivity. This value is important for the present invention, and the basis thereof will be described in detail later. When a high resistance adhesive layer is used as the surface resin layer 23, the thickness including the adhesive layer is preferably between 10 and 100 μm, and the resistance value is preferably 1010 Ω or more in surface resistance value.

These numerical values are also important for the present invention, and the basis thereof will be described in detail later.

Regarding the manufacturing method of the pressure roller 2, a PFA or FEP tube whose core metal and inner surface have been etched in advance is fixed in a cylindrical shape, and a liquid or low-viscosity conductive compound is placed between the core metal 21 and the tube 23. A method of manufacturing by casting silicone rubber and heating and curing it, a method of coating a PFA or FEP tube with an etched inner surface on a conductive silicone rubber roller that has been vulcanized and molded in advance, and then shrinking it by heating can be adopted as appropriate.

Next, the effects of the present invention will be described based on specific examples.

The image forming apparatus shown in FIG. 1 forms an electrostatic latent image by raster scanning a laser beam on a photosensitive drum 8 made of an organic photoconductor that has been negatively charged in advance, and performs reversal development using negatively charged toner. A laser beam printer was used that transferred a toner image onto a transfer material using a transfer roller to which a voltage was applied. The image forming speed is 60 mm/
It has the ability to print 10 sheets of A4 size transfer material per minute. The fixing device uses a heating roller 1 on which the core metal has an outer diameter of 29.9 mm and is coated with a PFA layer with a thickness of 30 um, and an appropriate amount of carbon black is mixed on the core metal with an outer diameter of 10 mm as the pressure roller 2. A conductive silicone rubber having a volume resistivity of 10 3 Ωcm was molded to a thickness of 6 mm, and a PFA tube having a thickness of 50 ALm was coated thereon. Using the laser beam printer mentioned above, this pressure roller was used as a transfer material on plain paper with a basis weight of 128 g/m'' and a polyester film.・Film for (head projector) (thickness 100 μm)
Offset performance was evaluated using At this time, the offset performance is evaluated by printing a horizontal line of 2 dots on the leading half of the transfer material in the feeding direction with a space of 5 dots.
Evaluation was made by determining whether the image on the rear half (which was performed at a scanning line density of 0 dpi) was transferred from the heating roller 1 to the transfer material again as an offset image.

As a result, no phenomena such as offset or wrapping of the transfer material occurred, and even though 300,000 sheets of A4 size paper were passed through, the pressure roller did not become dirty and no phenomena such as offset occurred. I was not able to admit.

The reason why this example has such excellent characteristics is considered as follows.

As shown in FIG. 2, the OHP film 211 has a transfer charge (positive in this embodiment) on the back side of the OHP film 211 and a photosensitive drum (not shown) on the surface (toner image side) of the OHP film 211. ) There is a charge of opposite polarity to the transfer charge that is ordered when separating from ). In general transfer materials, these charges of opposite polarity are neutralized through the transfer material, and transfer charges with a large amount of charge remain. However, OHP
In a high-resistance transfer material such as the film 21, the charges do not move in the thickness direction, so they remain on the front and back surfaces of each other. At this time, if the transfer charge leaks from the pressure roller 2, the OHP film will have an excessive charge of the same polarity as the toner, and a force will be generated to repel the toner. As a result, toner adheres to the heating roller 1, causing an offset.

In this embodiment, since the resistance of the surface layer of the pressure roller is sufficiently high, the charge on the back surface of the OHP film does not escape from the pressure roller, so that it is possible to sufficiently retain the toner on the surface of the OHP film. - On the other hand, with regard to the phenomenon in which the pressure roller 2 is charged, repelling the toner on the transfer material or causing the transfer material to wrap around the pressure roller 2, it is possible to prevent the pressure roller 2 from repelling the toner on the transfer material or by using conductive rubber for the elastic layer of the pressure roller 2. Even if the capacitance of the pressure roller 2 becomes large and an electric charge is generated on the surface of the pressure roller 2 due to frictional charging with the transfer material, the potential remains at a low level and repels the toner on the transfer material or wraps the transfer material around it. No more electrostatic force is generated. In addition, regarding the high durability of the pressure roller, the fluororesin layer on the surface has sufficient strength, and since it does not contain fillers, it has excellent mold release properties, so dirt does not adhere to it due to its durability. In addition, the elastic layer uses heat-resistant materials such as carbon black and metal powder that are resistant to deterioration to control resistance.
The resistance value does not change even after long-term use and has excellent environmental stability.
Offset performance etc. do not change either initially or due to environmental changes. In addition, in this embodiment, in order to prevent the pressure roller 2 from being charged by increasing the capacitance of the pressure roller 2, it is necessary to bring a conductive brush into contact with the surface layer of the fluororesin layer to release the charge. do not have.

The physical property values required to obtain the above-mentioned effects are as follows, according to studies by the present inventors.

1. The resistance value of the surface fluororesin layer needs to be such that it is difficult for the backside charge of high-resistance transfer materials such as OHP films to escape, and the higher the resistance value, the better, but in terms of physical properties, the contribution of the surface resistance is It needs to be large and have a surface resistance value of 1010Ω or more. At this time, the method for measuring the surface resistance value is
As shown in the figure, a voltage V of IOV was applied to the electrodes 31a and 31c arranged in the circumferential direction of the pressure roller 2 with a width of 10 mm, and the current flowing through the electrode 31b was measured. From the result, the outer diameter r of the pressure roller 2 was determined. , the surface resistance value R is calculated from the inter-electrode distance β (10 mm in this measurement) using the following formula.

2. The larger the capacitance of the pressure roller 2, the more the pressure roller 2
Because the charge accumulated on the surface becomes difficult to reach the surface potential,
The larger the capacitance, the better, and it needs to be 100 pF or more. At this time, the capacitance was measured as shown in FIG.
The capacitance between the electrode 4 having a width of mm was measured using an LCR meter (AG4304 manufactured by Ando Corporation) 42. In order to obtain the above capacitance, PFA, PTFE, FEP
When using a fluororesin such as, the fluororesin layer including the adhesive layer must be 100 gm or less, the resistance of the elastic layer must be sufficiently low, and the volume resistivity of the rubber layer used as the elastic layer must be It is necessary to use a material with a resistance of 107 Ωm or less.

[Example 2] FIG. 5 shows another example of the present invention, in which a pressure roller silicone rubber layer 512 is vulcanized and molded, and then a layer made of a mixture of fluororubber and fluororesin is coated as an adhesive layer 513. After that, the pressure roller 51 is obtained by spraying dispersion such as PFAFEP or electrostatically coating powder, and then heating and baking at a temperature equal to or higher than the melting point of the fluororesin.

Although the pressure roller 51 obtained in this way has a pure fluororesin layer 514 with no fillers mixed in, the electric charge on the surface layer is reduced due to the action of minute pinholes generated during coating. It has the characteristic of being attenuated. As a result, if the charge does not attenuate at all from the surface fluororesin layer 514, such as when several hundred sheets of transfer material are continuously passed through, the surface potential of the pressure roller 51 gradually increases even if the capacitance is large. However, although it does not generate enough electrostatic force to repel the toner on general transfer materials, it is especially
When a high-resistance transfer material such as a P film is used, the surface potential of the pressure roller 51 is neutralized, so the charge on the back surface of the transfer material may be partially lost and a slight offset may occur. In this embodiment, it is possible to avoid such a phenomenon.

Therefore, in this embodiment, since there is OH as in the previous embodiment, there is almost no leakage and no offset or the like occurs. On the other hand, the electric charge generated on the surface leaks due to minute pinholes generated during coating, so the surface potential of the pressure roller does not increase. However, in order to satisfy both characteristics, the surface fluororesin layer 514 It is preferable that the volume resistivity value is 10'4 Ωm or less. Further, in this example, the winding property of the transfer material was similar to that of the previous example, and although the durability was slightly inferior, it was at a level that caused no problem in practical use.

In order to obtain the above characteristics, the surface fluororesin layer 5
The thickness of the elastic layer 513 is preferably between 10 and 30 μm, and the elastic layer 513 having a hardness of 40 to 80 degrees (JIS A) is preferably 10 to 50 μm as an adhesive layer or intermediate layer between the elastic layer and the fluororesin layer. By providing a thickness of
The film properties of the surface fluororesin layer 514 are within a range that has sufficient strength and at the same time allows generation of appropriate pinholes.

[Embodiment 3] FIG. 6 is a schematic sectional view of a fixing device according to another embodiment of the present invention. In this embodiment, a diode 61 is installed in the heating roller 1.
The present invention is characterized in that a self-bias is selectively applied using a low-capacity rectifying element, such as, for example, using electric charges generated on the fixing roller 1 or electric charges induced on the heating roller 1 by the potential of the transfer material. In addition, the surface release layer 61 of the heating roller 61
2 is a 30 μm thick tube coated and fired;
Alternatively, a material coated with liquid PFA or PTFE to a thickness of 15 to 30 μm and then fired is used, and neither is finished by polishing.

The other configurations are the same as those in the first embodiment, so explanations will be omitted.

When such an unpolished heating roller 61 is used, if foreign matter gets mixed in during firing, offset may occur around that part, or the surface roughness is relatively rough (10
If the toner on the transfer material does not come into contact with the fixing roller (average point roughness Rz: 1 μm or more), the toner is attracted to the fixing roller by an electric field and flies away, making it easy for offset to occur.

Even with such a configuration, the pressure roller of the present invention generates less static electricity and is less likely to cause offset. However, in this embodiment, the heating roller 61 is grounded via a diode 62 in order to further enhance the effect of preventing offset. ing.

In this embodiment, since a negatively charged toner is used as the toner, the diode 62 is oriented as shown in FIG. With this configuration, a negative potential is generated in the heating roller 61 due to frictional charging with the transfer material or electric charge induced by the potential of the transfer material.
This makes it possible to prevent offset. Another advantage of this embodiment is that since the pressure roller 2 whose surface layer has the fluororesin layer 23 having high resistance is used, the electric potential appearing on the heating roller 61 does not leak through the pressure roller 2, so that transfer is possible. Even when a small-sized material is used, it is possible to always have an electric field that repels the toner. In addition, since the pressure roller 2 has a large capacitance and always maintains a stable potential, the potential of the heating roller 61 is not greatly affected by the potential of the pressure roller 2, and repels toner depending on the transfer material. It can have an electric field.

By providing the pressure roller 2 with the conductive elastic layer 22 and the high-resistance fluororesin layer 23 on the surface layer, it is possible to prevent offset even when the unpolished heating roller 61 is used. Furthermore, by combining the heating roller 61 with grounding with a low-capacity rectifying element such as a diode 62 having a self-bias effect, it becomes possible to fully exhibit the effect of providing the diode 62. In this embodiment, the diode 62 is used to apply a self-bias to the heating roller 61, but elements such as resistors, capacitors, and varistors may also be used. Also,
A similar effect can also be obtained by applying a bias voltage of the same polarity as the toner directly to the heating roller 61 from the power source.

[Embodiment 4] FIG. 7 is a schematic sectional view of a fixing device according to another embodiment of the present invention. In this embodiment, the outer diameter of the heating roller 71 is 25 mm when coated with a PFA layer, and the pressure roller 72 is coated with a conductive silicone rubber 722 having a thickness of 5 mm.
Covered with μm thick PFA tube 723, outer diameter 20m
m is used. Further, on the surface of the heating roller 71, a thermistor 3. A thermoswitch 73 is provided in the non-image area, and a non-contact separation guide 74 is provided with a gap of 0.3 mm. Furthermore, no cleaning member or the like is provided.

With this configuration, there is nothing that comes into contact with the heating roller 71 in the image area, and scratches caused by contact objects such as separation claws, thermistors, thermoswitches, etc., which conventionally determined the lifespan of the heating roller 71, can be avoided. This makes it possible to significantly improve the life of the heating roller 71, and it is possible to obtain a life of more than 300,000 sheets of A4 size paper.

In this embodiment, the pressure roller 72 is provided with a high-resistance resin layer on the conductive elastic layer of the present invention, and the thickness of the resin layer including the adhesive layer is 100 μm or less. By setting the diameter to 25 mm or less, the heating roller 7
The contact separation claw is removed from 1, and the transfer material is transferred to the heating roller 74 by the non-contact separation guide 74 at least in the image area.
It became possible to separate it from

This is because the pressure roller 72 is not easily charged, so there is no force to electrostatically repel the transfer material, so the conveyance path of the transfer material is stabilized. Also, under high temperature and high humidity conditions, where the stiffness of the transfer material tends to weaken. 1100 with almost no frictional charging
Because the conductive layer 722 exists through the thin high-resistance layer 723 of LL or less, the charge of the transfer material induces charges of opposite polarity on the back side of the high-resistance layer on the pressure roller side, resulting in electrostatic adsorption force. This serves to assist in separating the transfer material from the heating roller 71. In this way, it was previously difficult to separate transfer materials with a weak stiffness that had absorbed moisture under high temperature and high humidity conditions unless the outer diameter was 20 mm or less, but now it is possible to sufficiently separate transfer materials with an outer diameter of 25 mm. I made it. As a result, it is possible to obtain a sufficient nip even in printers and copying machines with relatively high paper feeding speeds, so it is possible to realize a fuser configuration in which the separating claw is removed, and the heating roller 71 pressure roller 72
It is possible to provide a fixing device having a durability of 300,000 sheets or more in both cases.

In the above embodiment, the pressure roller of the heat roller fixing device was explained as the roller having the elastic layer.
Even when used as a heating roller for fixing, the effects of the present invention can be sufficiently obtained if the elastic layer of the heating roller is thick (2 mm or more). Further, even when a belt-shaped thin fixing film is used instead of the heating roller for fixing, the fixing roller of the present invention can exhibit the same effect as a pressure roller.

In addition, in the above example, fluororesin was used for the resin layer, but
Resins such as silicone resins can also be used, and as the elastic layer, in addition to conductive silicone rubber, conductive rubbers such as fluororubber, urethane rubber, EPDM, etc., or silicone rubber, fluororubber, urethane, EPDM, etc. It is also possible to use a foamed conductive sponge.

[Effects of the Invention] As explained above, in the present invention, the winding of the transfer material can be avoided.
When a high-resistance transfer material such as a HP film or a general transfer material is used, offset can be prevented in either case, and a pressure roller with excellent long-term durability can be provided.

Furthermore, it is possible to use the unpolished fluororesin layer as the fixing roller, and it is also possible to remove the cleaning member for the fixing roller. Furthermore, if the outer diameter of the fixing roller is set to 25 mm or less, Since the claws for separating the transfer material can also be removed, it is possible to significantly reduce the cost of the fixing device.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the main parts of an image forming apparatus using a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the offset of an OHP film. FIG. 3 is a surface of a fixing roller. FIG. 4 is a diagram showing a method of measuring resistance; FIG. 4 is a diagram showing a method of measuring capacitance of a fixing roller; FIG. 5 is a schematic cross-sectional view of a fixing roller according to another embodiment of the present invention; FIGS. FIG. 2 is a schematic cross-sectional view of a fixing device according to another embodiment of the present invention. 1... Fixing roller 2... Pressure roller 22... Conductive rubber layer 23... Release layer 50 Fig. 6

Claims (8)

[Claims] (1) In a fixing roller having a surface resin layer on the elastic layer, the elastic layer has a volume resistivity of 10^7 Ωcm or less, and the resin layer has a surface resistance of 10^1^0 Ω or more and a thickness of 100 μm. A fixing roller characterized by the following: (2) The fixing roller according to claim 1, wherein the elastic layer is made of silicone rubber containing a conductive substance, and the resin layer is made of fluororesin. (3) The fixing roller according to claim 1 or 2, wherein the elastic layer is provided on a conductive base material. (4) In a fixing device that includes a heating body and a pressure roller that forms a nip with the heating body and has a surface resin layer on the elastic layer, the volume resistivity of the elastic layer is 10^7Ωc.
m or less, and the surface resistance value of the resin layer is 10^1^0
A fixing device having a thickness of Ω or more and a thickness of 100 μm or less. (5) The fixing device according to claim 4, wherein the elastic layer is made of silicone rubber containing a conductive substance, and the resin layer is made of fluororesin. (6) The fixing device according to claim 4 or 5, wherein the elastic layer is provided on a conductive base material. (7) The fixing device according to any one of claims 4 to 6, wherein the heating body is a heating roller, and a core metal of the heating roller is grounded via a self-bias element. (8) The fixing device according to any one of claims 4 to 7, wherein the heating body is a heating roller, and the heating roller has a surface layer formed of an unpolished fluororesin layer.